Biomarkers play a critical role in cancer diagnosis and treatment. Antibodies represent an important class of biomarkers with many advantageous features such as good stability, accessibility in biofluids, and easy detection. There has been extensive research on identifying changes in antibody levels to protein antigens; however, analysis of antibodies that binding carbohydrate antigens have been largely underutilized. Our carbohydrate microarray is well-suited to monitor the repertoire of anti-glycan antibodies in human serum and to study changes in their levels in response to disease or treatment of disease. The high-throughput approach can be used to identify new single biomarkers or to identify combinations of changes or profiles that are useful as biomarkers. We have been developing and validating a carbohydrate microarray assay for measuring antibody levels in human serum. The assay and array technology is being applied to a) characterizing the natural collection of antibodies in healthy individuals, b) evaluating natural changes in antibody levels over time, c) identifying changes in antibody levels in cancer patients, and d) identifying changes in antibody levels induced by vaccination or other cancer treatment.